疲劳损伤临界值分析

通过对疲劳过程和疲劳失效的临界状态的分析，提出疲劳失效判据应与损伤程度和应力水平两个因素有关，并在试验的基础上建立了一个剩余强度退化的对数模型。根据疲劳过程中材料强度退化的事实及其规律。分析了损伤临界值与循环应力水平之间的关系，给出了一般应力水平下疲劳损伤临界值的范围，对于随机疲劳问题，给出了损伤临界值的分布规律。

Analysis on Critical Fatigue Damage

irstly, the paper presented the multi-value character of the critical fatigue damage in differentloading condition and pointed some pitfalls of the conventional cumulative fatigue damage models andrelated failure criterions. Then through analysis on fatigue proecess as well as critical state of fatiguefailure , it is propsed that fatigue failure is determined by both cumulative fatigue damage and currentstress level, and two or more parameters are needed in fatigue failure criterion. In order to constructsuch a failure criterion, a logarithmic model is developed to describe residual strength desradation lawby means of fatigue test result of a normalized carbon steel. Accreding to the fact that residual strensthof the material continuously reduced in fatigue process, fatigue damase is defined as the ratio of thedecrement of material strensth to its original value, this damage parameter has an obvious physicalmeaning and is measurable, and is comlparable with the damage definition of damage mechanics, too.According to the logarithmic residual strength degradation model and the fatigue damage parameter , arelationship between critical fatigue damage and cyclic stress level is studied. The range of critical fa-tigue damage is given for constant amplitude fatigue and its probability distribution function is obtainedfor random fatigue.